Several molecular biomarkers have been studied in ER + luminal BC in an attempt to refine its classification with emphasis on ER-related genes including progesterone receptor (PgR), forkhead box protein A1 (FOXA1), GATA binding protein 3 (GATA3) and trefoil factor 1 (TFF1) [7–9]. The gene discussed is PGR; the disease is breast cancer.